An example of the above infusion pump system is disclosed in the patent literature PTL 1 filed by the inventor of the present invention. The infusion pump system of PTL 1 comprises (a) an infusion bag (as a medical solution container) containing a predetermined medical solution; (b) an infusion tube (as an infusion line) connected to the infusion bag and configured for drawing of the medical solution drawn therethrough and out of the infusion bag; (c) a pump unit driven by a piezoelectric element and configured to discharge the medical solution via the infusion tube; (d) an operation panel for inputting setting values including a volume of infusion (as an infusion speed) or a total volume of infusion; and (e) a control circuit.
The control unit includes (i) a settings switching part configured to select the setting values of the volume of infusion or the total volume of infusion that have been input; (ii) a flow measurement part configured to measure an infusion speed of the medical solution flowing through the infusion tube; (iii) a comparison part configured to compare the setting value of the volume of infusion with the measured infusion speed; and (iv) a pump control part configured to control the pump unit on the basis of the result of comparison by the comparison part.
In this infusion pump system, the setting value of the volume of infusion (a reference infusion speed) is input by operating the operation panel, and the discharge speed of the pump unit is controlled by the control circuit with reference made to (i) the setting value of the volume of infusion and (ii) the infusion speed of the medical solution flowing through the infusion tube. The control is made such that the infusion speed of the medical solution becomes equal to the setting value and thereby infusion is automatically done with a predefined volume of infusion, in other words, at a predefined infusion speed.
The configuration and operation of the infusion pump in the above-described infusion pump system is described below with reference to FIG. 5.
Referring to FIG. 5, there is schematically illustrated a piezoelectric pump provided in the pump unit. The pump unit 20 (infusion pump) includes a piezoelectric pump unit 21 constructed by a plurality of the piezoelectric pumps 22 arranged in series with each other, in parallel with each other, or in combination of series and parallel connections.
The piezoelectric pump 22 includes a piezoelectric element 221; an electrode 222 disposed upon and in close contact with the piezoelectric element 221; a glass plate 223 configured to be placed in oscillation by the piezoelectric element 221 in a direction indicated by an arrow S; a chamber 224 containing the medical solution; an inlet hole 225 through which the medical solution is drawn into the chamber 224; and an outlet hole 226 via which the medical solution is discharged from the chamber 224.
The piezoelectric element 221 in the piezoelectric pump 22 is adapted to oscillate in accordance with voltage and frequency applied to the electrode 222, and the glass plate 223 is adapted to oscillate in response to the oscillation of the piezoelectric element 221. As a result, the volume of the chamber 224 changes.
When the volume of the chamber 224 is reduced by the oscillation of the glass plate 223, the inlet hole 225 becomes smaller (more restricted) than the outlet hole 226. Accordingly, the flow resistance P2 created in the medical solution flowing toward the outlet hole 226 becomes smaller than the flow resistance P1 created in the medical solution flowing toward the inlet hole 225. As a result, the medical solution in the chamber 224 flows from the inlet hole 225 to the outlet hole 226 (in a direction indicated by an arrow R).
When the volume of the chamber 224 is increased by the oscillation of the glass plate 223, the medical solution is drawn via the inlet hole 225 into the chamber 224, and the piezoelectric element 221 is placed in desired oscillation by adjustment of the voltage and frequency applied to the electrode 222, so that the medical solution is discharged via the outlet hole 226 at a desired discharge speed. In this manner, the medical solution discharged via the outlet hole 226 of the piezoelectric pump 22 is infused via the infusion tube 31 into an inside of a body of a patient H such as a blood vessel IV (vein).
Since the above-described piezoelectric pump 22 has an open structure (i.e., has a flow path extending in a continuous manner without intervening valves provided therein), the discharge speed is susceptible to be influenced by a destination of discharging of the medical solution. For example, if the destination of the discharging of the medical solution is the vein, then a venous pressure created in the vein acts as the flow resistance P3 upon the medical solution. Even when predefined voltage and frequency are applied to the electrode 222 by the control circuit such that the discharge speed of the piezoelectric pump 22 becomes equal to the setting value of the volume of infusion, there may exist a gap between the medical solution delivered (infused) to the vein and the setting value of the volume of infusion.
Also, in the above-described infusion pump system, if there is the gap between the setting value of the preselected volume of infusion and the actual measurement of the infusion speed, the control circuit is configured to automatically change the discharge speed of the piezoelectric pump (i.e., the pump unit) so that the infusion speed of the medical solution becomes equal to the setting value of the volume of infusion.